1. Field of the Invention
The present invention relates to a radiographic image conversion panel and a method for producing the radiographic image conversion panel.
2. Description of Related Art
In earlier technology, so-called radiography in which a silver salt is used in order to obtain a radiographic image has been utilized. However, a method for imaging a radiological image without using a silver salt has been developed. That is, a method for imaging by absorbing a radiation ray transmitted through a subject in a phosphor, thereafter, exciting the phosphor with a certain type of energy, and radiating the radiographic energy accumulated in the phosphor as a fluorescence is disclosed.
Concretely, a radiographic image conversion method in which a panel provided with a photostimulable phosphor layer on a support and either or both of visible ray and infrared ray is used as excitation energy has been known (for example, see U.S. Pat. No. 3,859,527 specification).
As radiographic image conversion methods using photostimulable phosphors having higher luminance and higher sensitivity, a radiographic image conversion method using a BaFX:Eu2+ system (X: Cl, Br, I) phosphor (for example, see Japanese Patent Laid-Open Publication No. Sho 59-75200), a radiographic image conversion method using an alkali halide phosphor (for example, see Japanese Patent Laid-Open Publication No. Sho 61-72087), and an alkali halide phosphor containing metals of Tl+, Ce3+, Sm3+, Eu3+, Y3+, Ag+, Mg2+, Pb2+, In3+ as co-activators (for example, see Japanese Patent Laid-Open Publications Nos. Sho 61-73786 and Sho 61-73787) are developed.
Furthermore, recently, in analysis of diagnostic imaging, a radiographic image conversion panel having higher sharpness has been required. As a method for improving the sharpness, for example, attempts for improving sensitivity and sharpness by controlling the shape of photostimulable phosphors have been made.
As one of these attempts, for example, there is a method for using a photostimulable phosphor layer having a fine quasi-columnar block formed by depositing a photostimulable phosphor on a support having a fine concavoconvex pattern (for example, see Japanese Patent Laid-Open Publication No. Sho 61-142497).
Further, a method for using a radiographic image conversion panel having a photostimulable phosphor layer in which cracks between columnar blocks obtained by depositing a photostimulable phosphor on a support having a fine pattern are shock-treated to be further developed (for example, see Japanese Patent Laid-Open Publication No. Sho 61-142500), further, a method for using a quasi-columnar radiographic image conversion panel in which cracks are caused from the surface side of a photostimulable phosphor layer formed on a face of a support (for example, see Japanese Patent Laid-Open Publication No. Sho 62-39737), furthermore, a method for providing cracks by forming a photostimulable phosphor layer having a void on an upper face of a support according to deposition, and thereafter, by growing the void according to heat treatment (for example, see Japanese Patent Laid-Open Publication No. Sho 62-110200), and the like are suggested.
Furthermore, a radiographic image conversion panel having a photostimulable phosphor layer in which an elongated columnar crystal having a constant slope to a normal line direction of a support is formed on the support according to a vapor phase deposition method (for example, see Japanese Patent Laid-Open Publication No. Hei 2-58000) is suggested.
Recently, a radiographic image conversion panel using a photostimulable phosphor in which Eu is activated to a ground material of alkali halide such as CsBr or the like is suggested. Particularly, it becomes possible to derive a high X-ray conversion efficiency, which was unable to be obtained in earlier technology, by using Eu as an activator.
However, with a host crystal of alkali halide, when its composition is made to increase X-ray absorption, the strain of the crystal becomes large. Even though it has high luminance, the luminescence distribution in luminescence wavelength expands and the luminescence becomes broad since it has many luminescence levels. The effect of this broad luminescence becomes remarkable when Eu is used as an activator. Although the luminance is high, the persistence and response deteriorate since the distribution at the luminescence levels is expanded.
When alkali halide is used in CR detector as a radiographic imaging system, the problem of this persistence is large. As the radiographic imaging system, the problem is that a constant time is required to be taken before the reading after X-ray exposure as effect of instant persistence. As the effect of photostimulated persistence, the problem is that the contrast of reading deteriorates according to the persistence. Further, the persistence also affects reading rate (reading cycle and utilization frequency).
Therefore, improvement relating to properties, which measure up to improvement of luminance and sharpness required from market as a radiographic image conversion panel and to speeding up, has been required.
On the other hand, diffusion of Eu according to heat is remarkable, and there is a problem such that the existence of Eu in a ground material is distributed unevenly according to dispersion and the like since the vapor pressure under vacuum is also high. Thereby, it has not yet been in practical use at market since it is difficult to obtain an aimed high X-ray conversion efficiency.
Particularly, in activation of rare-earth element capable of obtaining a high X-ray conversion efficiency, with respect to film formation under vacuum, uniformizing is more difficult problem than vapor pressure property. Further, in manufacturing method, there is a problem such that the existence state of the activator becomes nonuniform since a number of heat treatments, such as heating of raw materials when preparing the photostimulable phosphor layers, heating of substrates (supports) at the time of vacuum deposition, and annealing (strain relaxation of substrates) treatment after film formation, is performed to these photostimulable phosphor layers formed by vapor phase growth (deposition).
Therefore, improvement in uniformity relating to manufacturing, which measures up to improvement of luminance and sharpness required from market as a radiographic image conversion panel, has been required.
Particularly, the effect of nonuniformity of evaporation raw materials in thermal expansion of base materials at the time of heating and cooling is large in phosphor layer face property. Effects such that its adhesiveness deteriorates when the film thickness becomes thick, that cracks are easily generated, and the like can be recognized remarkably in macroscopic and also in fine structure. These effects are a problem.